1. Field of the Invention
The present invention generally relates to an engine exhaust gas purification apparatus that reduces and removes nitrogen oxide (NOx) exhausted from a diesel engine, gasoline engine or the like installed in a moving vehicle, by injecting a reducing agent, which is mixed with high-pressure air, into the exhaust gas upstream side of a reducing catalytic converter through an injection nozzle. In particular, it relates to an exhaust gas purification apparatus that prevents erroneous detection of clogging by detecting clogging of the injection nozzle based on the pressure of the high-pressure air and the temperature of the injection nozzle.
2. Description of the Related Art
Several exhaust gas purification apparatuses have been proposed as system for removing harmful matter, especially NOx, from exhaust gas discharged from an engine, to purify the exhaust gas. Japanese Unexamined Patent Publication No. 2000-27627 discloses a typical exhaust gas purification apparatus for a diesel engine. In such an exhaust gas purification apparatus, a reducing catalytic converter is provided in an exhaust system of an engine, and a reducing agent, which is mixed with high-pressure air, is injection-supplied to an exhaust gas passage on the upstream side of the reducing catalytic converter to thereby create a catalytic reduction reaction between the NOx in the exhaust gas and the reducing agent in order to purify the NOx to harmless elements. The reducing agent is stored in a reducing agent tank in a liquid state at normal temperatures, and the required amount is injection-supplied from the injection nozzle. In the reduction reaction, ammonia, which has good reactivity with NOx, is used, and as the reducing agent, a urea water solution, an ammonia water solution, or other reducing agent water solution, that is hydrolyzed and produces ammonia easily, is used.
In this type of exhaust gas purification apparatus, there are situations in which the reducing agent, urea for example, is deposited during injection, and clogging the injection nozzle, so that sufficient reducing agent cannot be injection-supplied to the exhaust gas passage. To counter such a problem, an incorporation of such a system for detecting the pressure change in the high-pressure air can be considered in order to determine if the injection nozzle is clogged.
However, in the case where clogging of the injection nozzle is determined by detecting the pressure change in the high-pressure air, there is concern that the above-mentioned incorporation of the pressure detecting system may also be sensitive to detecting pressure changes in the high-pressure air produced by minute clogging, which is not a major cause of damage to the injection-supply of reducing agent, for example clogging in which deposited reducing agent will be melted easily by an increase in temperature in the injection nozzle and disappear, so that the system erroneously detects this as clogging of the injection nozzle.